Recovery of zinc values



Patented June 30, 1942 UNITED STATES PATENT OFFICE I v sensor I to a a:

' No 1mm Application February 3, 1940,

r Serial No. 311,131

Claims. (Cris-9'1 This invention relates to methods for recovering values from galvanizers sal ammoniacskimmings, and is particularly-directed to processes whereby residues substantially free 01 ammonium compounds and solutions containing zinc chlo'--.

- and replaced. The skimmings, which are known to the art by such terms as "galyanizers waste," sal skimmings and spent flux" always contain, along with other constituents, zinc metal, iron compounds, and zinc and ammonia associated monium chloride content of such leach liquors as abovedescribed and then to add ammonium hydroxide in such concentrations that the so.- called ammoniated zinc chlorides or zinc amminochlorides" may be crystallized out of 'the,

- hence, diammoniated zinc chloride cannot be with chlorine as various chlorides, oxychlorides,

or double salts. The ammonia and combined zinc constituents may conveniently be represented as their single chlorides, but such representalore proposed. In one process, the skimmings are milled with hot water, metallic zinc and dross are screened oil, and the zinc chloride liquor thus obtained is used for p rposes wherethe presence of substantia amounts of ammonium chloride is not a detriment. However, itthis liquor is evaporated to dryness, the ammonium chloride content of the salts so obtained is not sumciently high to permit their economical use as galvanising fluxes, since for maximum lite and mixing action a galvanizing flux preferably should contain about three molecules oiammonium chloride for 'each molecule of zinc chloride and the salts obtained by this method will ordinarily have less 40 than the desired ratio.

Ithasbeentobuilduptheammonium chloride content oi a purified extraction liqconsidered to be an economical galvanizing flux.

j Processes for recovering values rrom sal skimmings which involve preparation of ammoniated zinc chlorides iurther suffer from the disadvantage that all the soluble zinc values are recovered in association with substantial amounts 01' ammonia or ammonium chloride. As already point-. ed out, in such processes it-is necessary that ammonia or ammonium chloride be added in direct proportion to the zinc chloride in the sal skim.- mings, since no provision is made for recovering the zinc chloride in relativel pure form. The

0 building up or the amount of zinc chloride-am monium chloride double salt or ammoniated zinc chloridewhich must be produced causes the entire process at times to become economically unbalanced. Conversely, processes whichpermit isolation or the zinc chloride in relatively pure form are economically balanced at all times since there is a wide variety 0!- uses for zinc chloride uncontaminated with substantial amounts of am- 7 monimn chloride.

not such as above described by adding ammonium ammonium chloride suitable for use as galvanischloride so that a suitable galvanizing ilux can be crystallized from the liquor. This procedure isnot only expensive, but the amounts crammonium chloride which must be added increase in direct proportion to the amount oizinc chloride inthe process. A continuous increasein the amount of zinc chloride-ammonium chloride double salts which must be produced thus re- ,ults, since no provision is made tor separation of the zinc chloride constituent.

in; fluxes. Metallic zinc can be recovered by screening or sedimentation, either before or after filtering oil the insoluble residues, and after iiitration the balance 01 the residues can be converted to zinc chloride merely y dissolution in hydrochloric acid. The zinc chloride so obtained has an ammonium chloridecontent well below the maximum limit permissible ior most Ilsa.

Bytheapplicationotthepoimyinlthasalsobeenproposedtobuilduptheamfi vcntionto the recovery or val es f o s jaonium chloride double salt having a zinc chloride-ammonium chloride ratio which is best adapted to the needs of a galvanizing flux. The

onium hydroxide added is converted to emnionium chloride and this is also recovered as a double salt with zinc chloride. The portion of zinc chloride constituents not used in making the double salt is recovered as zinc chloride of salable quality. Metallic zinc is recovered di rectly, in accordance with considerations previ ously known. It is therefore evident that none of the constituents of the sol slrlmmines is wasted. butali are recovered in a form for which there is an established demand.

In the operation of my novel processes for treating sal shines the concentrations of am= monium chloride and ammonium hydroxide are maintained low enough to prevent the formation of ammoniated zinc chloride. The ammonium hydroxide is permitted to be only strong enough to precipitate as a basic Zinc chloride a prede= termined portion of the soluble nnc values present in the sol shimmings. The manner of determining the proportion of soluble zinc values to be so precipitated will be fully set forth in the following description of my invention.

The nature of my novel processes for recover= ins values from sal slrimmings and their manner of application may be better understood from the following illustrative examples.

Example 1 The purpose in this example was to prepare from galvanizers sal slslgs a galvanizing flux having nine, ammonia, and chlorine present in the ratios indicated by the empirical formula ZnCh-BNHrCl and the proportions of materials used were governed accordingly.

The sal shimrnines used had a total water soluble zine content equivalent to 32.2 per cent 221012 and a total ammonia content equivalent to lbs per cent NrhCl. Thus, water soluble zinc chloride and soul chloride were present in the proportions necessary to. form the em pirical compound ZiiCh-QdtSNHsCl.

An extraction solution made by dissolving 13.9 parts by weight of aqueous ammonia containing 23.? per cent Nl h in t3"! parts by weight of a liquor containing 12 parts of zinc ammonium chloride having approximately the empirical formula ZnChdNHuCl, the amount of sonic added being calculated to be suficlent, after the extraction step, to precipitate basic zinc chloride. This liquor, before the addition of the sonic, was representative of the wash liquor obtained by washing a filter press calze produced accord his to the processes of this example, as will be described below.

Ill

aesaeos total ammonia calculated as onium chloride (NHAGD, the molecular proportion being very close to ZnClz-3Nl-hCl. The extraction liquor was slightly basic to methyl orange, and was accordingly neutralized with hydrochloric acid to the methyl orange end-point before crystallization.

By evaporation and crystallization of this extraction liquor a product was obtained which had an average composition represented by the well below the maximum permissible in com mercial grades of zinc chloride for most purposes.

When sal skimmings are extracted with dilute ammonium hydroxide in accordance with a process of my invention, the amount of ammonium hydroxide used is so related to the zinc chloride content of the sol skimmings that a basic zinc chloride is precipitated. By control-- line the amount of basic zinc chloride formed, the ratio. of zinc chloride to ammonium chloride in the extraction liquor may be controlled. I have found that the proportion of dilute ammonium hydroxide required to produce a given zinc chloride-ammonium chloride ratio from a given lot of sal shimmings is dependent upon the total water soluble salts which are to be present in the extraction liquor, the proportion of amoni hydroxide increasing with the concentration of soluble salts. When the total soluble salts content of the extraction liquor is to be less than about 9.5 per cent, the proportion of sonic required may be calculated directly from the zinc chloride and ammonium chloride contents of the sal skimmings, but when the total soluble salts content is greater than about 9.5 per cent, the amount of ammonia required is proportionately increased.

When a liquor having a total soluble salts con-= tent less than about 9.5 per cent and a ratio znonzswrnei is desired, l have found that the amount of ammonia to use may be calculated from the expression X=.268Z-.228A, where X is the parts by weight of ammonium hydroxide (NEhOl-l) to add per one hundred parts of sal shimrnings and Z is the parts by weight of soluble zinc chloride (211012) and a is the parts by weight of onium chloride originally present one hundred parts by weight of sal skimmings. This expression, of course, only applies when a liquor ha a 1:3 molecular ratio is wanted. a liquor of 1:2 ratio and a total soluble salts content less than about as per cent is desired, 11 have found that the amount of ammonia to use can be calculated from the expression Z=229Z-291A where X, Z, and A have the same meanings as in the expression set forth s ove.

In process of my inventionit is not necessary that the extraction liquor contain zinc chloride and soul chloride in the exact ratio of the product which it is desired to crystallize ircm such liquor since the ratio of these constituents in the crystal will not always coincide 'with their ratio in the liquor from which the crystal is produced. For instance, upon crystallization at C. a liquor containing salts in the ratio ZnClz-2NH4Cl will at first give a crystal of empirical composition ZI1C12-3NH4CL This will diminish the ammonium chloride content of the liquor more rapidly than the zinc chloride con- -tent, and when the ratio of dissolved salts in the liquor has become ZnClz:i.5NH4Cl a crystal having the molecular ratio ZnCl2:2NH4Cl will be obtained. Thus, if the number of mols of ammonium chloride in an extraction liquor is not less than 1.5 times the number of mols of zinc chloride, at least some crystals of the double salt, ZnClz-3NH4Cl can be produced.

Since as pointed out above a product of 1:3-

ratio is particularly desirable as a galvanizing flux, I prefer to employ in my novel processes such proportions of reactants as will give an extraction liquor containing at least '1.5 mols of ammonium chloride per mol of zinc chloride. To make a liquor having this ratio according to a process of my invention, provided the total salts content of the extraction liquor is less than about 9.5 per cent, one would use an amount of ammonia calculated from the expression where Z is the parts by weight of soluble zinc chloride (ZnClz) and A is the parts by weight of ammonium chloride originally present in 100 parts by weight of the sal skimmings, and X is the parts by weight of ammonium hydroxide (NH-40H) to add per 100 parts by weight of the sal skimmings.

In the practical application of my novel processcs'it is economically advantageous to operate in a cyclic manner. Thus the mother liquor from one crystallization is combined with the extraction liquor from a subsequent batch, and further crystallization is effected. An alternative procedure is to crystallize the product continuously under suitable conditions. is done it is important that the ratio of ammonium chloride to zinc chloride in the extraction liquor be the same as in the product crystallized out, since otherwise ammonium chloride or zinc chloride will accumulate in the crystallization liquor and a product of varying composition will be obtained.

Whether a batch or cyclic operation is contemplated, I will ordinarily prefer to use such proportions of dilute ammonium hydroxide as will give a liquor having a 1:3 ratio.

It has already been shown in the foregoing discussion that the dilute ammonium hydroxide used for extracting sal skimmings according to a process of my invention shouldbe present in such a proportion that basic zinc chloride is precipitated in the extraction process. It has also been pointed out that the proportion of ammonium hydroxide required is dependent upon the total soluble salts content of the extraction liquor and that when this soluble salts content exceeds about 9.5 per cent the proportion of ammonium hydroxide required is disproportionately increased. I have found that if about 1.5

When this the stated range-namely, about 2.5 per cent, when the extraction temperature is high, and nearer the lower figure of 1.5 per cent when the extraction temperature is low-'-that is, below about F.

The application of a process embodying the above-described aspect of my invention is illustrated in Example 2.

Example 2 An extraction solution was made by mixing 26.55 parts by weight of ammonia solution containing 28.8 per cent NH: with 408 parts by weight of a liquor containing 32 parts of zinc ammonium chloride having approximately the empirical formula ZnClz-3NH4Cl. This liquor before the addition of the ammonia was representative of the wash liquor obtained by washing a filter press cake produced according to the processes of this example, as will be described below. To this basic extraction. solution there was added 200 parts by weight of sal skimmings, the analysis of which was the same as in Example 1. The mixture was agitated mechanically for thirty minutes at F. The insoluble material was then filtered off and washed, the wash liquor being kept separate from the filtrate.

' There was obtained 321 parts by weight of filtrate which upon analysis was found to have a total salt content of 25.5 per cent. Of this amount 48.0 per cent was total zinc calculated to zinc chloride (ZnClz). The total ammonia content calculated as NHiCl was 52.0 per cent. The molecular proportion of ZnClz to total ammonia present corresponded approximately to ZnClz-ZBNHrCl.

'It was noted that this extraction liquor was alkaline to methyl orange indicator. Accordingly, before attempting to concentrate and crys tallize this solution it was neutralized with muriatic acid to about the methyl orange endpoint. The liquor was then concentrated, crystallized, and a product was obtained which had the empirical formula ZnCh-3NH4CL The ammonium chloride content of the washed filter cake obtained as above described was determined to be .47 per cent on the basis of the dried cake. After removal of the metallic zinc from this press cake, the remainder of memsoluble material was converted to a commercially.

acceptable grade of zinc chloride by dissolving in muriatic acid.

The proportion of ammonium hydroxide used in Example 2 was about 28 per cent in excess of the proportion used in Example 1, and the extraction liquor had a total salts content approximately 16 per cent in excess of that of Example 1. Hence it will be seen that the amount 01 excess ammonium hydroxide used was about 1.8 per cent for each per cent by which the soluble salts content of the extraction liquor exceeded about 9.5 per cent.

It should be noted that when calculating the proportion of ammonia to use from the total salts content of the extraction liquor expected,

any unneutralized ammonium hydroxide in the droxide is actually present in dilute solution. in calculating the amount oi aqueous onium hydroxide solution to use account must be taken of the water added with the ammonium hydroxidle and its effect upon the concentration of total salts in the extraction liquor.

Although with higher concentrations of soluble salts in the extraction liquors obtained by a process of my invention it is necessary to use considerable amounts of excess ammonium hydroxide, it should be remembered that these excess amounts are based on the amounts used for extraction liquor containing less than about 9.5 per cent of soluble salts, and in any event the amount of ammonium hydroxide used is not sufiicient to be considered otherwise than as a dilute solution.

As a practical matter, when extracting galvanlzers sal skimmings with ammonium hydroxide in accordance with a process of my invention, it is preferable to use suficient water in the extraction so that the per cent total salts in the extraction liquor will be in the range of from about to about 30 per cent. More preferably this concentration should be not greatly in excess of about 20 per cent in order to facilitate washing of the filter calre and other such manipulations.

While I have shown particular applications of the processes of my invention for illustrative pur-= poses, it will be understood that without departing from the spirit of my invention, one skilled in the art may employ numerous specific modifications for recovering values from galvanizers sa-l slrimmings by extraction with dilute ammonium hydroxide.

i claim:

1. in a process for recovering values from galvanizers sal sltimmings containing insoluble material and zinc and ammonium chlorides in the ratio of less than 3 moles of ammonium chloride per mole of zinc chloride, the steps comprising treating the shimmings with a dilute ammonium essence 2. In a process for recovering values from galvanizers sal slrimmings containing insoluble material and zinc and ammonium chlorides in the ratio of less than 3 moles of ammonium chloride per mole of zinc chloride, the steps comprising treating the slrimmlngs with a dilute ammonium hydroxide solution, the amount and concentration of ammonium hydroxide in the treating solution being sumcient to precipitate at least a portion of the zinc chloride as basic zinc chloride but insumcient to form ammoniated zinc chloride from the zinc chloride, separating the insoluble material and precipitated basic zinc chloride from the treating solution, and crystallizing from the solution a zinc chloride-ammonium chloride double salt containing at. least 2 moles of ammonium chloride per mole of zinc chloride.

3. In a process for recovering values from galvanizers sal skimmings containing insoluble materialand zinc and ammonium chlorides in the ratio of less than 3 moles of ammonium chloride per mole of zinc chloride, the step comprising treating the sleimmings with a dilute ammonium hydroxide solution, the parts by weight of ammonium hydroxide used per hundred parts of sal skimmings being not substantially less than the amount calculated from the expression (.199Z-.339A) nor substantially more than the amount calculated from the expression (.2682- .228A), where Z is the parts by weight of soluble zinc chloride and A is the parts by weight of ammonium chloride originally present in the sal skimmings.

RAYMOND J. EZlll) a w. 

